Control and operation of SMES and SMES/PV systems

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Abstract

Applications, converter topologies, and control schemes are examined for
superconductive magnetic energy storage (SMES) systems. Diurnal load leveling for
electric utilities and compensation for fluctuations in photovoltaic (PV) power generation
are the primary applications discussed.

It is demonstrated that a SMES system implemented with standard AC/DC
converters offers energy storage capacity large enough, and dynamic response fast
enough, to compensate for PV fluctuations due to changes in weather conditions. The
method of control is developed so that the charging and discharging of the SMES system
are changed in response to PV fluctuations, and the combined SMESIPV power output is
smooth and controllable.

An innovative control scheme is introduced for SMES that can simultaneously
regulate real power and voltage independently without hardware modifications to the
standard ACIDC bridge arrangement normally used for coordinated control of real and
reactive power.

The combination of SMES and PV systems could benefit from DCIDC converters
that take advantage of the DC nature of both. It is established that DClDC converters can
respond with sufficient speed to handle variations in PV power. A converter topology is
devised where two DC/DC converters in cascade effectively maintain a PV array at its
maximum power point and simultaneously control a SMES system to compensate for PV
fluctuations.

An alternative cascade configuration of an AC/DC converter with a DCIDC
converter is proposed that could significantly reduce the reactive power requirements and
improve the operational characteristics of a large scale SMES system connected to the
utility grid.